Iodine-Catalyzed Highly Diastereoselective Synthesis of trans-2,6-Disubstituted-3,4-Dihydropyrans: Application to Concise Construction of C28-C37 Bicyclic Core of (+)-Sorangicin A

A novel iodine-catalyzed highly diastereoselective synthesis of trans-2,6-disubstituted-3,4-dihydropyrans have been achieved from delta-hydroxy alpha,beta-unsaturated aldehydes by treating with allyltrimethyl silane in THF at room temperature with good to excellent yields. This methodology has been successfully implemented for a concise asymmetric synthesis of C28-C37 dioxabicyclo[3.2.1]octane ring system of (+)-sorangicin A in 8 steps with 21% overall yield